The present invention relates generally to a theft prevention system in an automotive keyless entry system for locking and unlocking a vehicle door with an input code inputted from externally mounted push buttons. More particularly, the invention relates to a theft prevention system adapted to produce an alarm signal when the vehicle door is opened while the keyless entry system is maintained in a door-lock mode.
Conventionally, there are various theft preventive alarm systems for a door lock. Such theft preventive alarms associate or cooperate with a cam mechanism in a cylinder lock used for locking and unlocking the vehicle door. An alarm switch in such a system is provided adjacent to the cam mechanism so that the alarm switch is closed while the door is locked. If the vehicle door is opened without resetting the alarm switch, an alarm signal is produced to prevent the vehicle from being stolen. However, since the alarm switch is cooperable with the cam mechanism, if the cam mechanism in the door lock system can be placed in the unlocked position by a thief, the alarm switch can be turned off. This way, the conventional theft preventive alarm system cannot prevent door opening by way of operating the cam mechanism.